W0198

Miniaturized Kappa Goniometer for Macromolecular Crystallography. Gerd Rosenbaum, Structural Biology Center/CMB, Argonne National Laboratory, 9700 S. Cass Ave. Bldg 435D, Argonne, IL USA

A goniometer with kappa geometry has been designed and built specifically for macromolecular crystallography. The main feature is a miniaturized kappa stage made possible by the small weight of specimen and specimen holder.

The miniaturized kappa goniometer has the following features:

• no interference between kappa stage and an area detector for specimen-to-detector distances ≥ 100 mm, omega rotation angle of ±120° for distances ≥ 70 mm;

• 0.02 mm diameter sphere of confusion - necessary when dealing with very small crystals at third generation sources;

• small solid angle of shadow and inaccessible positions of the sample due to interference of the kappa stage with other objects in the sample area;

• rotation speed of 10 degree/s at 0.5% constancy and 0.4 s acceleration time for 0.05 s exposures of 0.2 degree fine slice frames every 2 seconds;

• precise synchronization between rotation angle and shutter opening and closing.

The kappa stage is mounted on a commercial high precision rotary table, designed for use in both horizontal and vertical orientation. This table provides the high precision rotation for data acquisition. The required crisp response and constant speed is delivered by a high output direct drive DC-motor, controlled by a closed-loop controller using feedback from a precision angular encoder. The kappa- and phi-motions are used for sample positioning only and are driven by miniature DC-motors equipped with integral encoders.